The invention relates to a ribbon, preferably a bonding ribbon for bonding in microelectronics, comprising a first layer comprising copper with a surface and at least a coating layer comprising aluminum superimposed over the surface of the first layer, and an intermediate layer. In a cross-sectional view of the ribbon, the area share of the first layer is in the range of from 50 to 96%, based on the total area of the cross-section of the ribbon. The aspect ratio between the width and the height of the ribbon in a cross-sectional view is in the range of from 0.03 to less than 0.8 and the ribbon has a cross-sectional area in the range of from 25,000 μm=2 to 800,000 μm=2. The intermediate layer, arranged between the first layer and the coating layer, comprises at least one intermetallic phase comprising material of the first layer and material of the coating layer. The invention further relates to a process for making a ribbon, to a ribbon obtained by the process, to an electric device comprising at least two elements and at least the ribbon, to a propelled device comprising the electric device and to a process of connecting two elements through the ribbon by wedge-bonding.
Bonding wires are used in the manufacture of semiconductor devices for electrically interconnecting an integrated circuit and a printed circuit board during semiconductor device fabrication. Further, bonding wires are used in power electronic applications to electrically connect transistors, diodes and the like with pads or pins of the housing. While bonding wires were made from gold in the beginning, nowadays less expensive materials, such as copper or aluminum, are used. While copper wire provides very good electric and thermal conductivity, wedge-bonding of copper wire has its challenges compared to wires made of aluminum. Moreover, copper wires are susceptible to oxidation of the wire.
With respect to wire geometry, very common are wires of circular cross-section. Another interesting geometry for bonding are ribbons which have a substantially rectangular cross-section. Both geometries have their advantages, making them useful for specific applications. Thus, both types of geometry have their share in the market. For example, ribbons have a larger contact area for a given cross-sectional area. However, bending of the ribbons is limited and orientation of the ribbon must be considered when bonding in order to arrive at acceptable electrical contact between the ribbon and the element to which it is bonded. Turning to bonding wires, these are more flexible to bending. However, bonding involves either soldering or larger deformation of the wire in the bonding process, which may cause harm or even destroy the bonding pad and underlying electric structures of the element which is bonded thereto.
Some recent developments were directed to bonding wires having a core and a shell, which is, for example, a coating layer. As core material, copper or gold are often chosen. With regard to the coating layer, aluminum is one of the more common choices. These core-shell bonding wires combine some of the advantages of copper wire and some of aluminum wire. Recent achievements make using standard wedge-bonding processes for such aluminum coated copper wires possible. Nevertheless, there is an ongoing need for further improving bonding technology with regard to the wire or the ribbon and the bonding processes.